1. Field of the Invention
The present invention pertains to mobile transmitter location and tracking systems. In particular, the present invention pertains to a centrally controlled tracking system used to locate and/or track material assets and/or personnel within a monitored area of control.
2. Description of the Related Art
The need to locate and track material assets and/or individuals within a predetermined monitored area of control is evident from a wide range of conventional mobile asset and/or personnel tracking systems. Typically in these systems, the asset or individual to be tracked is assigned a mobile, signal-emitting identification (ID) tag, embedded within a bracelet or other device, that is physically attached to the asset or individual to be monitored. The monitoring system, therefore, is able to track the asset/individual based radio communications received from its associated signal-emitting ID tag. Such monitoring systems vary significantly with respect to the nature of communications with the respective ID tags and the devices used to implement the chosen communication signal architecture.
Some conventional systems position at known locations interrogating transmitters/receivers that periodically transmit a poll request to one or more signal ID tags within the interrogating transmitters/receivers broadcast area. Mobile transmitter/receiver ID tags that receive a poll request signal respond by issuing a poll response signal back to the polling device. Such systems typically do not attempt to pinpoint the location of the ID tag, but instead, approximate the location of the asset/individual based upon the fixed location of the interrogating transmitter/receiver. Further, the ID tags and interrogators must both be capable of receiving and processing signals as well as generating and transmitting signals, thus increasing deployment and maintenance costs and decreasing overall system reliability due to increased complexity.
In other conventional systems, simpler devices that only receive signals are used instead of the interrogating transmitters/receivers discussed above and devices that only transmit a signal, either periodically or in response to a user initiated action, are used instead of the transmitter/receiver ID tags described above. However, the total cost of deploying and maintaining such systems remains high and the ability of such systems to simultaneously track large numbers of ID tags, or to timely track individual ID tags within a large pool of deployed ID tags remains limited. Further, such systems still rely upon a distributed network of signal processing receivers that have a fixed signal processing capacity and, therefore, are not capable of supporting large swells in ID tag movements.
Conventional tracking systems are typically limited with respect to the number of ID tags that can be simultaneously supported. Such limitations are typically due to the heavy communication traffic and/or signal processing associated with continually polling and/or processing signals received from each individual tag in the system. To handle high loads, complex, high-speed signal processing equipment is required, thus increasing system deployment costs, increasing system failures, and hence increasing down-time and maintenance costs. Often the required high-speed components must be distributed throughout the area of coverage, thereby forcing the capacity of the distributed system components to be sized on a worse-case-scenario basis (thereby increasing costs) or to accept limited capacity and/or decreased flexibility and/or compromising the ability of the system to respond to large asymmetrical shifts in ID tag populations. Such large shifts in population are most likely to occur under emergency conditions when the location tracking system is needed most.
Another deficiency associated with conventional asset/personnel tracking systems is the inability to protect against the loss, theft, or removal of a transmitter from the monitored area. Loss of ID tags is a serious concern because once the transmitter leaves the monitored area, the system control computer will be unable to determine its location. One way to mitigate the risk posed by such an event is to constantly scan for transmitters at the entrance/exit points to the monitored facility using RF-relays that are positioned at the entrances/exits of the installation. However, it is impractical in an installation with a large number of transmitters to scan for every transmitter at every entrance/exit point at a sufficiently high rate as to provide continuous, unbroken surveillance without substantially increasing the computational capability of the signal processing computer(s) tasked with monitoring these areas.
Hence, a need remains for a cost effective, high precision, modularly expandable asset/personnel tracking system that is capable of effectively safeguarding against loss of ID tag transmitter devices. The system must be capable of accurately locating an asset/person within any sized population within a monitored area, yet be comprised of cost effective, reliable and easily maintained equipment. Preferably, the system capacity would be modularly expandable from a central location and system capabilities/performance must not be adversely impacted by large shifts in the monitored ID tag population.